1. Field of the Invention
This invention relates to an automated solder ball grid assembly array and to a method of providing solder columns therein and the assembly.
2. Brief Description of the Prior Art
Typically, in accordance with the prior art, surface mounted electronic packages which are mounted on circuit boards have leads around the periphery of a surface of the package with the leads later being soldered to the board. Another type of packaging uses a pin grid array where the pins can be anywhere on a surface of the package rather than only at the perimeter, thereby permitting many more pins to be available in the same area as compared with the above described arrangement. A further type of prior art packaging is a ball grid array wherein an electronic package is provided with interconnect traces and solder balls thereon which are the means for connection. There is mismatch in such types of packaging between the printed circuit board which is typically FR-4 and the integrated circuit package which is ceramic, BT resin or filled epoxy novalac resin. Whereas leaded SMT packages have leads which can flex and absorb the mismatch, in ball grid array (BGA) the leads are rigid and the solder is subject to fatigue cracking. As the distance between mismatching materials (i.e., package and board) is increased, stress concentration is decreased within the material which connects the dissimilar materials. In order to compensate for some mismatch in thermal expansion between the electronic package, the printed circuit board and the solder ball connection of a package, it is desirable to make the connections as tall as possible to absorb some of the mismatch and stresses. Accordingly, the solder balls are sometimes replaced with solder columns to provide such tall connections as a column grid. Attachment of solder balls and/or solder columns is cumbersome and relatively costly with automation thereof being highly desirable.